Historically, perfumes have been prepared by dissolving fragrance oils in volatile alcohols, primarily ethanol, or in a mixture of ethanol and water. The industrialization of surfactants and the advances in colloid science have made possible the solubilization of fragrances in water by means of emulsification with surfactants. When an emulsion has a particle size of about 140 nm or less it is referred to as a microemulsion. The small size of these microemulsions containing fragrance oils results in perfume products that are clear or almost clear, and are not very different in appearance to conventional ethanol-based perfumes.
Microemulsions contain physical structures which can be described as swollen micelles, inversed micelles or continuous bi-layers. None of these structures are present in conventional ethanol-based perfume products.
The key benefit of water-based perfumes is a reduction in VOC's (Volatile Organic Compounds). Another benefit is the immediate perception of the intrinsic nature of the fragrance oils due to the absence of ethanol or ethanol-like alcohols. However, microemulsion water-based products tend to be foamy, sticky or even irritating to the skin due to presence of the surfactants required to solubilize the fragrance.
These drawbacks are magnified as the surfactant content increases. This content depends on the intrinsic efficiency of the selected surfactant system, the ease or difficulty of solubilization of the fragrance oil itself, and the total content of the fragrance oil in the final perfume product. In any case, T. J. Lin mentioned in Surfactants in Cosmetics, Surfactants Sci. Ser. Vol. 16, (1985), 29-52, that the practical preparation of these microemulsion products will need a ratio of surfactant solubilizer system to fragrance oil much greater than 1/1. There is therefore a need to make the microemulsions with low concentrations of skin compatible surfactants.
U.S. Pat. No. 5,374,614 discloses low VOC microemulsions for perfumery applications with reduced surfactant content. The surfactant system consists of a non-ionic fraction and an anionic fraction, which are also representative of other disclosures in the art, such as in U.S. Pat. No. 7,655,613
The non-ionic fraction in these documents is based on ethoxylated surfactants that are known for their excellent fragrance solubilization properties. Both patents disclose a long list of ethoxylated compounds. However, ethoxylated surfactants with molecular weights in the 400 to 1200 range and based on fatty acids, fatty alcohols, and even the alkyl phenol as disclosed in U.S. Pat. No. 5,374,614 and no longer used in consumer products, are known to disrupt the lipids of the stratum corneum. While acceptable for usage in many consumer and industrial products, where they may have functions in addition to fragrance solubilization, these surfactants are not very suited for perfume products for application to the skin or hair. Ethoxylated non-ionic surfactants with high molecular weight, such as the ethoxylated castor oil materials disclosed in U.S. Pat. No. 8,461,099, are very suited for perfumes for personal use.
The anionic surfactants disclosed in these patents are also known for their use in many personal cleansing products, household products, laundry products and detergent products in general. They are known to negatively interact with the corneocites of the skin to cause irritation, especially when left deposited on the skin, as it is the case of perfumery products intended for personal use.
Anionic surfactants are required in microemulsion-based fragrance products to offset the negative impact that the fragrance has on the cloud point of ethoxylated non-ionic surfactants. Non-ionic ethoxylates exhibit inverse water solubility behavior since they are less soluble as the temperature of the solution is raised. The temperature at which they are no longer soluble in water is called the cloud point. In the absence of fragrance, most of the ethoxylated materials disclosed in the prior art have cloud points above 50° C., but in the presence of solubilized fragrance the cloud point may be lowered to below 40° C., resulting in a product that may be hazy within the range of product usage or storage. The incorporation of anionic surfactants raises the cloud point above 40° C. in well balanced systems from a chemical viewpoint.
There is a need therefore to identify new surfactant systems capable of maintaining the cloud point of the water-based fragrance products above 40° C., while remaining clear down to 5 C, and with minimal or no irritation the skin, and reduced foaming and stickiness.
The present invention provides an unexpected and advantageous solution to all these requirements with the incorporation of skin compatible crypto-anionic surfactants that totally replace the anionic materials described as indispensable in the prior art.
An object of the present invention is therefore to provide new leave-on ethanol-free perfumed compositions which are stable to storage, in particular remain clear between 5 and 40° C. and which are non-irritant to the skin.